The present disclosure relates generally to protection for power supplies, and more particularly, to over power protection for switched mode power supplies.
Power supplies are commonly necessary for most consumer electronic appliances, for converting the power from power grids or batteries to the power with specifications suitable for an appliance. Superior in compact product size and conversion efficiency, switched mode power supply, among all kinds of power supplies, is globally adopted, especially in the consumer markets.
A power supple need not only provide suitable voltage or current meeting the required specification, but also prevent any accident or risk from occurring if abnormal events happen. These events, to name a few, include events of over power, over output voltage, overcurrent, and over temperature. Protection method to deal with these events must be considered during circuit design for a power supply.
Printers or notebook computers usually need extra high power output for a very short period of time. Most of time a printer, for example, operates in a standby mode or a signal transmission mode, in which all the mechanical devices of the printer stay static and the printer consumes very low or moderate power. Nevertheless, high power consumption is needed when a printer moves lots of mechanical devices or parts to perform printing, which common lasts only for a short period of time. Accordingly, a power supply for a printer needs to supply low or moderate output power “normally” and high output power “in pulse”. Two terms, including normal maximum power and peak power, are defined in this patent specification for a power supply, respectively referring to the maximum output power level it should supply when operating “normally”, and the maximum output power level it could when needed to provide extra power “in pulse”. It is costly effective to deem an occurrence of an over power event and trigger an corresponding protection response when a power supply continuously, for a period of time longer than expected, provides power more than the normal maximum power. U.S. Pat. No. 7,486,493, for example, discloses a switched mode power supply with over power protection.
In the specification of this patent application, devices or apparatuses with the same symbol refer to the devices or apparatuses with the same or similar function, structure, or characteristic. They might not be exactly the same, however. Their detail might not be restated in consideration of brevity, and could be understood or derived by a person skilled in the art according to the teaching herein.